Innovative and seamless interaction between player and non-player characters is a hallmark of Source-powered games. A sophisticated AI system allows NPCs to follow players, join in the fight, or engage the player in epic non-scripted battles. AI characters can run, fly, jump, crouch, climb stairs, and burrow underground.
Squads of AI characters operate together in epic non-scripted battles.

The sophisticated Pathfinding and Navigation System features a local avoidance system to help NPCs navigate around obstacles; a path cost system for fine tuning pathfinding choices; and dynamic and level designer-controlled path connections. The system recognizes the size of creatures—knowing where they can and cannot travel—and automatically accounts for all known methods of movement.

The AI Sensory System emulates human senses—vision, hearing, and even scent—to track and identify objects. The tunable system can be used for nearly limitless in-game mechanics and player challenges.

AI Relationships. Set a relationship between characters—an NPC, an NPC class, or player(s)—to influence behavior and action based on a variety of entities, such as hate, like, or fear.

Battle AI. Squads of AI characters can operate together and share knowledge about enemies. AI squad members track the status of each other—while one squad member is laying cover fire, another may recognize the opportunity to move or reload a nearly-empty gun cartridge.

I/O System. The flexible I/O system allows level designers to control AI without touching code.